This was an interesting one I came across recently; intermittently we would get reports of users receiving 404 errors and IIS default landing pages, as if SharePoint sites were not running/working on our Web Front End servers.

The SharePoint environment was 2x WFE, 2x Service Application and 1x SQL Server Reporting Services. The WFE servers were load balanced by a HLB. We’re using Host Named Site Collections, so have to manually configure IIS bindings on the Web Front End servers.

There were few errors that really explained what was going on – initially we thought it was a backup related issue, but I think that the backup simply exacerbated the issue rather than caused the issue.

The issue was pretty simple – the Request Management Service was proxying requests to other servers in the farm – noteably the Service Application and SSRS servers – where IIS is not configured for the HNSCs. On the Service Application servers we had an IIS site listening on all all IPs/host headers, HTTPS – this was for Central Admin. On the SSRS server there was no HTTPS provision – this explained the randome behaviour we were seeing:

IIS landing page on the HTTPS-enabled Service Application servers

404 errors on the non-HTTPS enabled SSRS server

Running some simple PowerShell commands we were able to exclude the Service Application and SSRS servers as targets from the Request Management Service configuration – commands taken from the blog above:

No need to perform an IIS reset, the commands take effect immediately. Alongside resolving the IIS default page/404 errors, we also noticed that the HNSCs loaded significantly faster after making this change.